Declaring List of multiple types in Kotlin

Question

I'm trying to have a mutable list which contains multiple types, says my data type and String. I have my data class MyObject

data class MyObject(val date: Date?, val description: String?)

So I expect something like list below:

var myList = mutableListOf<MyObject, String>()

Is there any way to archive it in Kotlin?

Answer 1

You can create a list that has the first common supertype of your two types as its type parameter, which in this case is Any:

val myList = mutableListOf<Any>()
myList.add("string")
myList.add(MyObject(null, null))

Of course this way you'll "lose" the type of the items that are in the list, and every time you get a list item you'll only know it by the type Any:

val item: Any = myList.get(0)

At this point you can make type checks to see what the type of the item is:

if (item is MyObject) {
    println(item.description)
}

Answer 2

In this specific case where the types are known and limited to two elements, I would use Pair:

var myList = mutableListOf<Pair<MyObject,String>>()

Full code snippet below:

import java.util.Date

data class MyObject(val date: Date?, val description: String?)

var myList = mutableListOf<Pair<MyObject,String>>()

   fun main(args: Array<String>) {
   val first = MyObject(Date(), "time1")
   val second = "info1"
   myList.add(Pair(first, second))
   println(myList[0])
}